Method and device for sealing boreholes

ABSTRACT

A device and method for sealing boreholes. Typically, a seismic test hole is sealed by covering a topping plug with water expansible material, such as bentonite, which seals the hole once it expands on exposure to water or moisture. The present invention provides a method and a device for sealing seismic holes, the device comprising a generally tubular water permeable sleeve filled with water expansible aggregate.

FIELD OF THE INVENTION

[0001] This invention relates to the sealing of boreholes, for exampleseismic boreholes, to prevent contamination of groundwater by water ordebris from the surface.

BACKGROUND

[0002] In seismic exploration there is a requirement to seal boreholesafter drilling in order to prevent contamination of groundwater and toprevent hydraulic communication between aquifers. As well, it isimportant to close up such holes to prevent injury to animals or peoplewho may not see the holes.

[0003] After a seismic borehole is drilled, a topping plug is placed inthe hole. A sealing material is added on top of the topping plug andsoil and topsoil is replaced on top of the sealing material. Bentoniteis often used as the sealing material since it expands when water isadded.

[0004] However, bentonite is usually packaged in large bags making itheavy and difficult to pour. The bentonite can spill on the ground nearthe borehole and therefore, is wasted and must be cleaned up. It is alsodifficult to ascertain how much bentonite was poured into the borehole.

[0005] Another method used to seal boreholes involves pouring concreteover the topping plug. The same problems that occur with bentonite canoccur with concrete, namely spillage and not knowing how much concretewas used. Spilled concrete is also messy and difficult to clean up.

[0006] This invention overcomes the problems identified with the priorart by providing pre-measured amounts of water-expansible aggregate,such as bentonite, in a water permeable sleeve that is easy to handleand insert into the borehole. The sleeve that contains the aggregateprevents spillage.

SUMMARY OF THE INVENTION

[0007] In a broad aspect, this invention provides a device for sealing aborehole comprising: a generally tubular water permeable sleeve, saidsleeve being closed at both ends, and water expansible aggregate, saidaggregate located within and contained by the sleeve, said sleevegenerally of a size and stiffness to maintain its shape when filled withsaid water expansible aggregate to permit insertion into a borehole andallow expansion of its contents on exposure to water.

[0008] In another aspect, this invention provides a method for sealing aborehole using the device as described in the first aspect consistingof: plugging the hole with a topping plug; sliding said device into saidborehole; and exposing said device to water whereby said aggregatematter expands and seals the hole on exposure to water.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 depicts a perspective view of a preferred embodiment of theinvention.

[0010]FIG. 2A is a longitudinal sectional view of a borehole containinga preferred embodiment of the invention, before the aggregate hasabsorbed any moisture.

[0011]FIG. 2B depicts a longitudinal sectional view of a boreholecontaining a preferred embodiment of the invention, after the aggregatehas expanded.

[0012]FIG. 3 depicts a longitudinal sectional view of a borehole filledwith three of the sealing devices as provided by a second embodiment ofthe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] In the preferred embodiment of the invention depicted in FIGS. 1,2A and 2B, the borehole sealing device 1 consists of a mesh sleeve 2made from polypropelene which is filled with crushed bentonite 3. Themesh sleeve 2 is closed at both ends with metal fasteners 4.

[0014] The sleeve 2 is generally tubular in shape after it is filledwith the aggregate 3. The diameter of the sleeve 2 is somewhat less thanthe diameter of the borehole 7, and of suitable length.

[0015] The material from which the sleeve 2 is made must be of suitablestiffness such that the generally tubular shape is maintained after itis filled with the aggregate so that it can slide into the borehole. Atthe same time, the material must allow water to flow through it to theaggregate and permit the aggregate to expand. A material that allowsexpansion in the horizontal plane of the generally tubular shape whileat the same time tending to restrict longitudinal expansion ispreferred. The sleeve 2 must be constructed from a material strongenough not to tear when filled with the aggregate 3 either duringhandling or insertion into the borehole. A mesh material of suitablestiffness and strength and with suitable sized openings is preferred.

[0016] Polypropelene mesh is durable even at cold temperatures and willresist tearing before the sealing device 1 is installed in a borehole.Polypropelene mesh is available in the form of a sleeve in a variety ofweights and diameters, and of indefinite lengths. A polypropelene meshsleeve material is selected of suitable diameter and weight. Thediameter will be less than the diameter of the borehole 7 after the meshsleeve 2 is filled with aggregate 3. The strength is sufficient toprevent tearing and the stiffness of the mesh will be sufficient tomaintain the generally tubular shape after filling with the aggregate 3.It is important that the mesh sleeve 2 does not bulge unduly under theweight of the aggregate 3, so that it can slide into a borehole 7.

[0017] Once the device is installed, the mesh sleeve 2 has no furtherfunction. However, it must allow the aggregate matter to expand acrossthe diameter of the borehole in order to seal it. The polypropelene mesh2 used in the preferred embodiment is flexible enough to allow for suchexpansion. An added advantage of polypropelene mesh sleeves is that theyare already commercially available in a variety of sizes. However, anymaterial that meets the requirements of holding the aggregate 3,maintaining its size and shape, allowing water to penetrate and allowingthe aggregate 3 to expand can be used. Examples of materials that couldbe used are suitable plastic mesh, such as polyethylene or nylon, orwire mesh.

[0018] Typically, about 20 inches of bentonite is used for closingseismic boreholes. Therefore, in the preferred embodiment the boreholesealing device 1, as shown in FIGS. 2A and 2B, would be approximately 20inches long. Once installed within a borehole 7, the top of the device 1would be being approximately 18 inches below the surface of the ground.However, the device can be made to various lengths depending on theneeds of the user and can be used at any depth.

[0019] Crushed bentonite is used as the aggregate 3 in the preferredembodiment. Bentonite is commonly used in industry to seal seismicboreholes. Crushed bentonite works well with the polypropelene meshsleeves because the bentonite chips are larger than the holes in themesh, thus ensuring the bentonite remains within the sleeve 2. However,any suitable water expansible aggregate could be used in this invention,so long as the aggregate size is larger than any holes in the sleeve.

[0020] The sleeve 2 must be closed at both ends in order to contain theaggregate 3. This can be done in any suitable manner. The type ofclosure must be strong enough to hold the weight of the aggregate.Examples of methods of closing the sleeve include: cinching each endwith tie wraps or crimps; folding and sealing the ends by heating orcrimping; heat fusing the ends; or lacing across the ends. In thepreferred embodiment, metal fasteners 4 are used to cinch the ends ofthe mesh sleeve 2. The fasteners 4 serve the purpose of holding thebentonite 3 within the sleeve 2 until at least after the device 1 isinstalled in a borehole 7.

[0021] Containing the pre-measured bentonite within the sleeve 2eliminates the need for the user to pour estimated amounts of bentonitefrom heavy bags. The use of metal for the fasteners 4 has the addedadvantage that a metal detector can later be used to locate the sealedborehole at a later date if necessary. Often there is a requirement forseismic boreholes to be inspected but they are difficult to locate oncethey are filled. If a metal fastener or the other metal accessory isused on the sealing device 1, the inspector can use a metal detector tolocate the boreholes.

[0022] To use the preferred embodiment of the present invention, a userslides the sealing device 1 into a borehole 7 after the topping plug 5has been installed. Then, if desired, the remainder of the hole isfilled with cuttings or other material 6. Water in the ground will causethe bentonite 3 to expand, thus sealing the hole. Later, if it isnecessary to locate the hole 7, a metal detector can be used to detectthe metal fasteners 4 used to close the ends of the sleeve 2 in thepreferred embodiment.

[0023] The mesh sleeve 2 holds a measured amount of the water-expansibleaggregate 3. Therefore, the user will know exactly the amount of theaggregate 3 placed into the borehole 7. The sleeve also provides amethod of easily handling the aggregate 3 and eliminates the need ofpouring it from a large bag into the borehole 7. Water or moisture canpenetrate through the sleeve to the aggregate 3, thereby permitting theaggregate to expand and seal the borehole. The diameter of the sleeve issmaller than the diameter of the borehole, so that it slides easily intoplace before the aggregate expands and fits snugly after the aggregatehas expanded. The sealing device 1 can be made to fit any size borehole.

[0024] In another embodiment of the invention shown in FIG. 3, more thanone sealing device 1 can be placed into a borehole 7. According to thisembodiment, any number of sealing devices can be stacked on top of eachother. FIG. 3 shows three sealing devices 1 in the same borehole 7. Theadvantage of using more than one sealing device is that each sealingdevice can be made so that it is a weight and length that can reasonablybe handled by workers who are sealing the boreholes. As well, thesealing devices 1 can be made to any size that is practical forshipping. In this embodiment, to achieve a seal of a desired length, auser inserts the number of sealing devices 1 needed to add up to thenecessary length.

1. A device for sealing a borehole comprising: a generally tubular water permeable sleeve, said sleeve being closed at both ends, and water expansible aggregate, said aggregate located within and contained by the sleeve, said sleeve generally of a size and stiffness to maintain its shape when filled with said water expansible aggregate to permit insertion into a borehole and allow expansion of its contents on exposure to water.
 2. A device for sealing a borehole according to claim 1 wherein said sleeve is mesh.
 3. A device for sealing a borehole according to claim 2 wherein said mesh sleeve is made of polypropelene.
 4. A device for sealing a borehole according to claim 1 wherein said aggregate is bentonite.
 5. A device for sealing a borehole according to claim 2 wherein said aggregate is bentonite.
 6. A device for sealing a borehole according to claim 3 wherein said aggregate is bentonite.
 7. A device for sealing a borehole according to claim 1 wherein at least one end of said sleeve is closed using a metal fastener.
 8. A device for sealing a borehole according to claim 2 wherein at least one end of said sleeve is closed using a metal fastener.
 9. A device for sealing a borehole according to claim 3 wherein at least one end of said sleeve is closed using a metal fastener.
 10. A device for sealing a borehole according to claim 4 wherein at least one end of said sleeve is closed using a metal fastener.
 11. A device for sealing a borehole according to claim 5 wherein at least one end of said sleeve is closed using a metal fastener.
 12. A device for sealing a borehole according to claim 6 wherein at least one end of said sleeve is closed using a metal fastener.
 13. A method for sealing a borehole using the device of claim 1 consisting of: plugging the hole with a topping plug; sliding said device into said borehole; and exposing said device to water; whereby said aggregate matter expands and seals the hole on exposure to water.
 14. A method according to claim 13 whereby more than one device is slid into the borehole. 